Electrolytic deposition of copper from acid solutions.



F. E. STUDT. ELECTROLYTLC DEPOSITION OF COPPER FROM ACID SOLUTIONS.

APPLICATION FILED JULYIB. I916.

Patented Mar. 26,1918;

4 W Dr FR ANZ EDWARD STUDT, OF LONDON, ENGLAND.

ELECTROLYTIC DEPOSITION OF COPPER FROM ACID SOLUTIONS.

Specification of Letters Patent.

Patented Mar. 26, 1918.

Application filed J u1y 18, 1916. Serial No. 109,992.

' tion of copper from acid solutions, and has for its object the provision of a more efficient and economic process than those. hitherto proposed for the commercial recovery of copper from acid solutions or electrolytes even when these contain a comparatively larqge amount of iron.

he invention is particularly applicable to electro-leaching processes in which copper ores are leached by means of acid liquors and the copper subsequently recovered from the liquors by electrolysis as in the equation:-

in which reaction the sulfur dioxid acts as a depolarizing agent by reason of its oxidation by means of the anodic oxygen which would be evolved and cause polarization and rise in the voltage of the electrolytic cell were no reducing agent (such as S0 pres-- out as in the equation:

The sulfur dioxid, when acting as a depolarizer, becomes a source of sulfuric acid for use as a leaching agent in copper extraction from the ores.

A difiiculty in the practical working of this process arises from the fact that when acid liquors act upon copper ores, the iron compounds, as well as other basespresent, are also taken into solution to a large extent and collect in the electrolyte from which the copper is being deposited.

The iron ta en up from such ores is generally partly in the ferric state and when sulfur dioxid is introduced into such liquors it tends to reduce the ferric iron to the ferrous state as in the equation:

' but the reduction of any large amount of the comparative slowness of the reaction at ordlnary temperatures, while at higher temperatures the amount of the reducing agent WhlCh the liquors can take up is very limited.

When sulfur dioxid is present in an electrolyte containing ferrous salts, then the latter also act as depolarizing agents, thus:

so giving rise to further ferric salts which will also tend to be reduced b SO as above. In such solutions there will be both ferrous andsulfur dioxid depolarization and the resultmg cell voltage will depend upon which of these two reagents becomes the dominant depolarizer and will be considerably greater when the ferrous reaction is the most prominent than when the reverse is the case.

Ferrous depolarization is also very objectionable because of the highly corrosive action which the resulting ferric salts exert upon the cathode copper thus:

Ou-l-Fe, s0 =CuSO,+2FeSO,

so that the copper deposited by electrolysis is partially returned to the electrolyte causing current wastage and low ampere efficiency, and this effect is very appreciable even when the ferric iron is present in quite small percenta e.

Hence it wil be seen from the foregoing that grave disadvantages arise from the occurrence of ferrous depolarization during electrolysis, even when sufiicient time has been allowed for the reduction of ferric salts (taken from the ores) before entering the electrolytic vats, and that any method which will tend to suppress this ferrous depolarization and accentuate the sulfur dioxid depolarization will result in lower cell voltage and higher current efficiency and thus efi'ect a large saving in the amount of power reuired for electrolysis, and it is this suppress1on of ferrous depolarization and accentuation of sulfur dioxid depolarization during the electrolysis of copper liquors carrying iron in solution which is the important feature of my invention.

This invention may be said, therefore, to consist broadly of a process by means of which the electrolysis of high iron electrolytes for copper deposition is carried out with sulfur dioxid as depolarizing agent, and ferrous depolarization almost or entirely suppressed so that little or no ferric salts are formed during electrolysis.

- and also steam-which is employed :pri-

In order to accomplish this the electrolyte should carry as much sulfur as can be taken up from the pure gas at the working temperature and should be as free as possible from ferric salts before entering the depositing tanks, and means should, moreover, be

provided whereby the electrolyte is continuously agitated particularly across the faces of the anodes. A further condition which should be observed is that the current density must not be too high and in this connection it may be stated that about 13 amperesper square foot of active anode surface will be found possible in practice.

The temperature of electrolysis should be between about 120 to 130 Fahrenheit or 49 to 53 degrees centigrade.

In practically carrying out the invention I propose to employ liquefied sulfur dioxid gas,the liquefied gas being preferable though not essential, and I accomplish the liquefaction by passing the sulfur burner gases through a cooling apparatus and thence passing the cooled as throu h a refrigerator in which the sul ur dioxid gas will be condensed or liquefied, the waste gases being taken off by exhaust fans or any suitable form of apparatus. The liquefied sulfur dioxid gas will be passed to a suitable reservoir, and by means of supply pipes leading to the electrolytic depositing tanks the pure gas will ass to these tanks under pressure varying fi'om two to four atmospheresdepending upon the temperature of the reservoir-much in the same way that steam passes from a steam boiler. The absorption of the sulfur dioxid as by the electrolyte will take place in the epositing tanks themselves with the consequent elimination of absorption towers and their accessories, and the further advantage that the absorption of the gaswill take place just when and where it is required, and the supply will be maintained as it is bein used by depolarization so that no interme iate, replenishment will be required even when the series of depositing tanks is a long one.

In order to produce the necessary agitation and circulation of the electrolyte I propose to make use of the sulfur dioxid gas marily for the purpose of insuring correct temperature conditions. To accomplish. this I propose to arrange a grating of lead i es located on the floor of each of the deposltmg tanks and connecting pipes from these in'gs will be connected to the sulfur d1oxid and steam'mains,'separate valves bein provided for separately regulating an controlling the gas and steam supply. The pipes orming the gratings within the depositing tanks will be perforated or provided with ejection nozzles. The pipes of the gratings will be so located and the perforations or nozzles arranged at such angles that the escaping gas and steam will tend to impinge angularly upon the faces of the anodes so that the electrolyte will be continuously circulated and the maximum agitation will occur across the anode faces. The steam passes through the same grating pipes as the gas and this has the advantage that the steam will tend to clear the perforations or nozzles of any crystallization de osits from the solution which would be lia le to choke such perforations or nozzles. Means may be provided for readily expelling any of the electrolyte or solution or steam condensation from the pipes within the tank should any leakage into them occur as a result of the gas pressure within them falling from any cause.

In the accompanying drawings I have illustrated diagrammatically the manner in which the process can be carried into practice, Fi re 1 being a diagrammatic elevational view of the apparatus.

Fig. 2 is a plan view with a section taken through one of the electrolytic tanks and showing the connections of the sulfur dioxid and steam supply pipes to the grid like piping within the tanks. 7

Fig. 3 is an enlarged section through one of the pipes of the grid like pipe structure,

ing apparatus 3, wherein the burner gases are condensed and pass in liquefied form through the pipe 4 to the sulfur dioxid reservoir 5, the waste gases being drawn off by an exhaust fan or other suitable apparatus. From this reservoir the sulfur dioxid passes under pressure through the main 6 to the electrolytic tanks 7. The numeral 8 designates a steam supply pipe leading from a steam generator or any other convenient source 0 trolytic tanks grid hke pipe structures 9 are provided and these grids are located upon the floors of the tanks and connection from the sulfur dioxid and steam pipes is made to these grid structures by means of the pipes 10 having branch connections 11 and 12, the

branch 11 connecting up to thesulfur dioxid main 6, and the branch 12 connecting to the steam supply. Within the elec-v steammain 8. Each of the pipes 11 and 12 provided. The pipes of the grid like pipe- ,structures are provided with perforations or nozzles indicated by the numeral 9, and these perforations or nozzles are bored or arranged at an angle diagonally of the tank so that the gas and steam passing through the perforations set up not only agitation but continuous circulation of the liquid in the tanks. Upon reference to Figs. 3 and 4: of the drawings, it Will be seen that the pipes are arranged to lie beneath the oathodes 14 and the escaping gas and steam tends to impinge upon the faces of the anodes l5, and thus effect agitation across the anode faces.

It Will be understood upon reference to Fig. 1 that the acid liquors or solutions are supplied to the head tank 16 from the leaching tanks by the pipe 17, and these liquors flow continuously through the series of electrolytic depositing tanks 7 to a sump 18 whence they are returned again to the leaching tanks.- Thus the liquor leaves the depositing tanks and tanks saturated with sulfur dioXid gas and therefore in a condition to best effect the reduction of ferric salts in the one during the period in which the leaching takes place and so reduces the chance of ferric salts being directly introduced into the depositing tanks. In order to effect satisfactorily this reduction of the ferric salts prior to the liquor entering the depositing tanks it will be found desirable in practice to extend the leaching period beyond that actually required to get the copper in the one into the solution, and usually a period of from ten to fourteen hours will be found effective, but it will be understood that the period process may passes to the leaching required will depend upon the conditions obtaining. It will also be appreciated that any desired number of depositing tanks may be arranged in series and that any suitable be utilized for obtaining the sulfur dioxid gas.

It Will be seen from the foregoing that my improved process involves as its essential characteristics the employment of pure sulfur dioxid gas preferably obtained from sulfur burner gases and the provision of means for introducing the pure gas directly to the de positing tanks, While a further important feature of the invention resides in the employment of the gas-in some cases, together with steam used primarily for obtaining the desired temperature conditionsfor the physical agitation and circulation of the electrolyte.

What I claim and desire to secure by Letters Patent is:

A process for the recovery of copper by electrolysis which consists in introducing sulfur dioxid gas directly into an electrolyzing vessel provided With anode and cathode elements during the electrolysis and in such a manner that the sulfur dioxid gas is directed against the faces of the anode and serves to effect circulation and agitation of the electrolyte across the anode faces to suppress ferrous depolarization and to accentuate sulfur dioxid depolarization.

In testimony whereof I affix my signature.

FRANZ EDWARD STUDT. 

